Polyacetal resins, which are engineering plastics, have excellent mechanical property, sliding property, frictional and wearing properties, chemical resistance and the like, and have been widely used in basic parts for automobiles, OA machines and the like. A polyacetal resin exhibits highly crystalline properties due to the regular primary structure thereof, and the application of the polyacetal resin is expanding mainly in the field of injection molding. In recent years, attempts are made to apply the polyacetal resin having the above-mentioned excellent properties to an extrusion use, particularly to fiber and film uses.
In plastic fibers and fiber assemblies comprising the same, conventionally, nylon and polyester have been mainly used. Particularly, in the field where a chemical resistance and a sliding property are required, fluororesin fibers have been used. However, nylon and polyester are not satisfactory in their sliding properties, and hence are desired to be further improved in the sliding properties. On the other hand, a fluororesin is an expensive material, and further has low aggregate force between molecules such that the molecular chains of fluororesin are unlikely to undergo orientation in spinning or stretching, so that it is difficult to obtain a fluororesin fiber having a practical mechanical strength. Thus, the fluororesin fiber does not satisfy both the required physical properties and the cost of production.
With respect to the polyacetal resin having excellent sliding property, frictional and wearing properties, and chemical resistance, like conventional general synthetic fibers, the production of a polyacetal resin fiber is attempted, and high sliding property and frictional and wearing properties of the polyacetal resin in a fiber form, which are comparable to the bulk property of the polyacetal resin, have been confirmed (for example, patent document 1 and non-patent document 1). Patent document 2 discloses stearic acid lubricants, and, as modifiers, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, glycerol, a silicone oil, a fatty acid amide, and a fatty acid ester, and has a description showing that, by adding to a polyacetal resin a lubricant or a modifier in an appropriate amount, the polyacetal resin is increased in fluidity, so that the stringiness of the resin upon melt spinning is improved.